Abstract
We developed free-standing nitrogen-doped carbon nanofiber (CNF) electrodes incorporating Co/CoOx nanoparticles (NPs) as a new cathode material for removing Acid Orange 7 (AO7; a dye for wool) from wastewater by the heterogeneous electro-Fenton reaction. We produced the free-standing N-doped CNF electrodes by electrospinning a polyacrylonitrile (PAN) and cobalt acetate solution followed by thermal carbonation of the cobalt acetate/PAN nanofibers under a nitrogen atmosphere. We then investigated electro-Fenton-based removal of AO7 from wastewater with the free-standing N-doped-CNFs-Co/CoOx electrodes, in the presence or not of Fe2+ ions as a co-catalyst. The electrochemical analysis showed the high stability of the prepared N-doped-CNF-Co/CoOx electrodes in electrochemical oxidation experiments with excellent degradation of AO7 (20 mM) at acidic to near neutral pH values (3 and 6). Electro-Fenton oxidation at 10 mA/cm2 direct current for 40 min using the N-doped-CNF-Co/CoOx electrodes loaded with 25 wt% of Co/CoOx NPs led to complete AO7 solution decolorization with total organic carbon (TOC) removal values of 92.4% at pH 3 and 93.3% at pH 6. The newly developed N-doped-CNF-Co/CoOx electrodes are an effective alternative technique for wastewater pre-treatment before the biological treatment.
Highlights
Water pollution continues to be one of the greatest challenges worldwide
As PAN is a polymer with nitrogen (N) atoms in its chain, it is used as N-source for carbon nanofiber (CNF) doping [62]
Designing metal NPs embedded on/inside N-doped-CNFs is of great interest as electrode materials because they offer many applications for energy conversion and storage and environmental remediation
Summary
Water pollution continues to be one of the greatest challenges worldwide. To date, many different water pollutant types (i.e., inorganic, organic, and biological) have been described [1,2,3]. Electro-Fenton oxidation is an IEO process in which organic pollutants in wastewater are degraded by ·OH radicals generated by the Fenton reaction (Equation (1)) between electro-Fenton reagents (e.g., Fe2+ ions) and H2 O2 Such H2 O2 molecules are produced by electrochemical reduction in dissolved O2 (Equation (2)), supplied by the continuous bubbling of O2 gas at the cathode. The N-doped-CNF-Co/CoOx electrodes have several advantages, including large surface area and low cost, low weight, easy handling, high chemical resistance, high thermal stability, and good conductivity They can combine adsorption and electrochemical indirect degradation of hazardous organic compounds either through the production of H2 O2 from oxygen reduction (Equation (2)) or the electro-Fenton process in presence of a catalyst (Equation (1)). O2 adsorption/adsorption energy at the electrode surface and an improvement in the electrocatalytic properties of the surface toward oxygen reduction reaction [57,58,59]
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